Mass spectrometers can be used to provide information about unknown sample compounds referred to as analytes. The mass-to-charge ratio information derived from spectrometry study, usually in the form of a mass spectrum, is used to positively determine the empirical chemical formulas of the analytes under investigation using analytical software (calculators). In the past, this determination has typically involved mathematical calculation of exact masses of all possible combinations of chemical elements. In view of the fact that large molecules can comprise an almost infinite number of possible combinations of elements, conventional calculators often allow the user to input constraints on certain parameters to limit the number of potential candidates for the empirical formula.
For example, the elements used, the minimum and/or maximum number of each element, whether the mass being searched is an odd/even or neutral species (for neutral loss from a fragmentation), possible adducts such as the molecule plus a proton, the molecule plus a potassium or sodium (all positive ions), the molecule minus a proton or the molecule plus an acetate or formate ion (all negative ions) can all be specified as constraints. Conventional calculators may also allow the user to specify a confidence limit or tolerance for the calculation.
In addition, some calculators provide functionality for determining relative abundances of isotopes present in a spectrum. The relative abundances are calculated from the known natural abundance of each isotope of each element in the empirical formula and the number of those elements. The relative ratios can then be compared to the measured ratios to test for correspondence.
However, to date, even when all the functionality of calculation software is employed and all reasonable constraints specified, too many potential candidates for the analyte ion are output by the software. A technique is needed that readily narrows down the number of potential candidates using information available from the mass spectrum and provides also provides a means to confirm otherwise error-prone results.